Albert Casullo

The leading arguments against the existence of a priori knowledge are addressed. The opposing arguments fall into three broad categories: conceptual arguments, which offer an analysis of the concept of a priori knowledge and allege that no cases of knowledge satisfy the conditions in the analysis; radical empiricist arguments, which offer radical empiricist accounts of knowledge of propositions alleged to be knowable only a priori; and incompatibility arguments, which maintain that a priori knowledge is incompatible with epistemic naturalism. This chapter contends that the negative arguments fail: the conceptual arguments impose implausible conditions on a priori knowledge; the radical empiricist accounts do not establish that the propositions in question are not also known a priori; and the incompatibility arguments fail to show that a priori knowledge is incompatible with either of the two leading forms of epistemic naturalism: philosophical and scientific.

The leading arguments supporting the existence of a priori knowledge fall into three broad categories: conceptual arguments, which offer an analysis of the concept of a priori knowledge and maintain that some knowledge satisfies the conditions in the analysis; criterial arguments, which identify criteria of the a priori, such as necessity, certainty, and irrefutability, and maintain that some knowledge satisfies the criteria; and deficiency arguments, which allege that radical empiricist theories of knowledge are deficient in some respect, and that the only remedy for the deficiency is to embrace the a priori. This chapter contends that these arguments fail: the conceptual arguments involve implausible conceptions of a priori knowledge; the criterial arguments involve false epistemic premises; and the deficiency arguments fail because theories endorsing the a priori suffer from the same deficiencies alleged to plague radical empiricism.

This chapter examines two conceptions of a priori justification: S’s belief that p is justified a priori if and only if S’s belief that p is nonexperientially justified; and S’s belief that p is justified a priori if and only if S’s belief that p is nonexperientially justified and cannot be defeated by experience. Two criteria are introduced to evaluate them: continuity with historical precedent, and coherence with generally accepted concepts and principles in the theory of knowledge. It is argued that although historical precedent does not favor either analysis, several theoretical considerations favor over. coheres better with the standard treatment of related epistemic concepts, highlights the central epistemic question raised by the theory of a priori knowledge, and satisfies a plausible criterion of adequacy regarding a priori justification; it leaves open the possibility of empirical knowledge of propositions knowable a priori.

This chapter addresses two questions: Is there synthetic a priori knowledge? Is the analytic/synthetic distinction cogent? The epistemic significance of the first derives from the assumption that synthetic a priori knowledge raises difficult explanatory problems that are circumvented by analytic a priori knowledge. The epistemic significance of the second derives from the assumption that if the analytic/synthetic distinction is not cogent, then the cogency of the a priori/a posteriori distinction is also doubtful. It is argued that both assumptions are false, and that resolving the controversies surrounding these two questions is not necessary to answer the primary epistemological questions about a priori knowledge.

This chapter provides a taxonomy of widely endorsed conditions on a priori justification. The conditions fall into two broad categories: epistemic, which includes defeasibility, strength, and source conditions; and nonepistemic, which involves the concepts of analyticity or necessity. Two major claims are argued: nonepistemic conditions are neither necessary nor sufficient for a priori justification, and if a theory imposes epistemic conditions on the a priori that differ from those it imposes on the a posteriori, they must be supported by independent argument or rejected as ad hoc. Two defensible conditions on a priori justification emerge: justification by a nonexperiential source, and justification that is not defeasible by experience.

This chapter articulates the requirements of fallible a priori justification. It distinguishes two senses of fallibility: c-fallibility, justification that does not guarantee truth; and p-fallibility, justification that is defeasible. It argues that although these senses are logically independent of one another, there are some significant relations between them mediated by the concepts of self-revision, overriding defeater, and undermining defeater. It is shown that several alternative fallibilist accounts of a priori justification face difficulties that are avoided by the account defended in Chapter 2.

In “A Priori Knowledge,” Albert Casullo asks whether there is a priori knowledge. He ultimately defines a priori knowledge as true belief with a priori justification, where a belief is a priori justified if it is nonexperientially justified. Armed with this definition, Casullo evaluates several traditional arguments for and against the existence of a priori knowledge. He concludes that the traditional arguments reach an impasse by arguing on a priori grounds that the opposite position is deficient. A successful way to defend a priori knowledge, he argues, would be to find empirical evidence that supports the existence of nonexperiential sources of justification.

E. J. Lowe offers an account of modal knowledge that involves two primary theses. First, the basis of modal knowledge is essential knowledge, and the source of essential knowledge is grasp of essence. Second, all empirical knowledge ultimately depends on some modal knowledge. This article assesses Lowe’s account and defends four conclusions. First, there is a tension in Lowe’s account of grasp of essence; it wavers between an undemanding version, which holds that grasp of essence requires no more than our ordinary understanding of propositions, and a more demanding version, which holds that it requires rational insight into necessary relationships between essences. Second, both versions face serious challenges. Third, Lowe’s account of knowledge of essence does not provide a basis for modal knowledge. Fourth, Lowe’s supporting argument for his second thesis contains two significant gaps and the principles necessary to close the gaps reveal further tensions in his epistemological views.

Kant contends that necessity is a criterion of the a priori—that is, that all knowledge of necessary propositions is a priori. This contention, together with two others that Kant took to be evident—we know some mathematical propositions and such propositions are necessary—leads directly to the conclusion that some knowledge is a priori. Although many contemporary philosophers endorse Kant’s criterion, supporting arguments are hard to come by. Gordon Barnes provides one of the few examples. My purpose in this chapter is to articulate and examine his argument. I have two goals in doing so. The first is to uncover several significant gaps in the argument. The second is to show that it suffers from a common defect in rationalist arguments. If the argument were successful against empiricist accounts of modal knowledge, it would apply with equal force to extant rationalist accounts of such knowledge. Hence, the cost of refuting modal empiricism is modal scepticism.

In Necessary Beings, Bob Hale addresses two questions: What is the source of necessity? What is the source of our knowledge of it? He offers novel responses to them in terms of the metaphysical notion of nature or, more familiarly, essence. In this paper, I address Hale’s response to the first question. My assessment is negative. I argue that his essentialist explanation of the source of necessity suffers from three significant shortcomings. First, Hale’s leading example of an essentialist explanation merely asserts that the nature of an entity explains some necessity, but leaves unexplained how it does so. Second, his essentialist explanation of particular necessities introduces new necessities that remain unexplained. Third, Hale’s version of essentialism presupposes a controversial metaphysical theory of properties, for which he offers no defense.

Christopher Hill contends that the metaphysical modalities can be reductively explained in terms of the subjunctive conditional and that this reductive explanation yields two tests for determining the metaphysical modality of a proposition. He goes on to argue that his reductive account of the metaphysical modalities in conjunction with his account of modal knowledge underwrites the further conclusion that conceivability does not provide a reliable test for metaphysical possibility. I argue (1) that Hill’s reductive explanation of the metaphysical modalities in terms of the subjunctive conditional does not yield a reductive explanation of knowledge of metaphysical modality in terms of knowledge of subjunctive conditionals, and (2) that his account of modal knowledge is at odds with his contention that conceivability does not provide epistemic access to metaphysical possibility.

In his seminal paper, Content Preservation, Tyler Burge defends an original account of testimonial knowledge. The originality of the account is due, in part, to the fact that it is cast within a novel epistemic framework. The central feature of that framework is the introduction of the concept of entitlement, which is alleged to be a distinctive type of positive epistemic support or warrant. Entitlement and justification, according to Burge, are sub-species of warrant. Justification is the internalist form of warrant, but entitlement is epistemically externalist. My focus in this paper is Burge’s conception of entitlement, and there are three primary issues that I wish to address. What is the relationship between entitlement and the more traditional concept of justification? In what sense is entitlement epistemically externalist? Has Burge introduced a new epistemic concept or merely coined a new term for a familiar epistemic concept?

For much of the past two millennia philosophers have embraced a priori knowledge and have thought that the a priori plays an important role in philosophy itself. Philosophers from Plato to Descartes, Kant to Kripke, all endorse the a priori and engage in a priori reasoning in their philosophical discussions. Recent work in epistemology and experimental philosophy, however, has raised questions about both the existence of a priori knowledge and the centrality of the a priori for philosophy. This collection of essays aims to advance the discussion of the a priori and its role in philosophy. The contributors include a mix of young and established philosophers, including some of the most prominent voices in philosophy today.

There are four approaches to analyzing the concept of a priori knowledge. The primary target of the reductive approach is the concept of a priori justification. The primary target of the nonreductive approach is the concept of a priori knowledge. There are two approaches to analyzing each primary target. A theory-neutral approach provides an analysis that does not presuppose any general theory of knowledge or justification. A theory-laden approach provides an analysis that does presuppose some general theory of knowledge or justification (call it the background theory). Those who embrace a theory-laden analysis incur a special burden: they must separate the features of their analysis that are constitutive of the a priori from those that are constitutive of the background theory. My goal is to illustrate how the failure to separate these features leads to erroneous conclusions about the nature of a priori knowledge.

Kripke claims that there are necessary a posteriori truths and contingent a priori truths. These claims challenge the traditional Kantian view that (K)  All knowledge of necessary truths is a priori and all a priori knowledge is of necessary truths. Kripke’s claims continue to be resisted, which indicates that the Kantian view remains attractive. My goal is to identify the most plausible principles linking the epistemic and the modal. My strategy for identifying the principles is to investigate two related questions. Are there compelling general supporting arguments for (K)? Are there decisive counterexamples to (K)? My investigation uncovers two intuitively plausible principles that are not open to decisive counterexamples but which enjoy no compelling independent support.

Radical empiricism is the view that experience is the only source of knowledge. Hence, radical empiricism denies the existence of a priori knowledge. Its most famous proponents are John Stuart Mill and W. V. Quine. Although both reject a priori knowledge, they offer different empiricist accounts of the knowledge alleged by their opponents to be a priori. My primary concern in this paper is not with the cogency of their positive accounts. My focus is their arguments against a priori knowledge. My goal is to establish that although they offer very different arguments against the existence of a priori knowledge, each of their arguments suffers from a common defect. They both fail to appreciate the phenomenon of epistemic overdetermination and its role in the theory of knowledge.